DESCRIPTION:(provided by applicant)The entry of HIV-1 into cells requires interactions between the viral Env protein, CD4 and a coreceptor. While binding to CD4 is required for efficient virus infection, attachment of virus to the cell surface can be mediated by interactions with a variety of molecules, only some of which have been well characterized. Attachment to the cell surface per se can be a limiting step in the entry pathway. In vitro, infection of cell lines and PBMC by HIV-1 can be enhanced by inclusion of polycations in the virus inoculum or by centrifuging virus onto the cell surface. Infection of activated T-cells can also be enhanced by first binding HIV-1 to dendritic cells (DCs). After removing unbound virus, addition of activated T cells results in very efficient transmission of virus to these cellular targets. Recently, a type lI integral membrane protein termed DC-SIGN has been shown to mediate binding of HIV-1 to DCs. DC-SIGN contains a C-type (i.e. calcium-dependent) lectin domain that mediates this process. Because DCs migrate from peripheral mucosal tissues to lymph nodes, it has been proposed that HIV uses DCs as carriers, allowing the virus to access lymphoid tissue. More generally, the discovery of DC-SIGN raises the possibility that other highly specific virus attachment factors exist. Indeed, we have found that DC-SIGNR, which shares 77 percent amino acid identity with DC-SIGN, also supports HIV binding and transmission. DC-SIGNR is expressed on endothelial cells in lymph nodes, liver, and the placenta, while DC-SIGN is expressed on DCs and some types of macrophages in vivo. The ability of DC-SIGN and DC-SIGNR to bind virus with high affinity, to augment lymphocyte infection, and their expression on cells in mucosal surfaces and the placenta where transmission occurs leads us to hypothesize that these proteins facilitate viral binding to cells, and that once bound, virions are modified and/or protected, and ultimately presented more efficiently to key target cells that initiate viral propagation and dissemination in the host. In this proposal, we will pursue four Specific Aims that will explore the structure, function, and expression patterns of DC- SIGN and DC-SIGNR. Furthermore, we will develop reagents that will enable us to test the role of DC-SIGN in sexual transmission of virus using the rhesus macaque model. We propose to take a highly collaborative approach employing the skills and expertise of the Doms and Hoxie labs, as well as collaborations with other laboratories so that these questions can be addressed quickly and efficiently through the pursuit of 4 Specific Aims.